Garden Pest?

Having moved from the countryside to a house with a very overgrown garden in the city, I have found black jumping insects living in the soil in my greenhouse and under pots outside. They look like shrimps or fleas and are about 5mm long . When disturbed they wriggle and jump and quickly dissapper into the soil. A search of Google images suggests they may be Terrestrial amphipods. I thought these were only found in warmer climates. I am in Exeter in Devon. Anyone any ideas about what they are and more importantly will they harm plants or can they be left in peace?

Alison, probably Arcitalitrus dorrieni, a non-native species of amphipod (a crustacean, not an insect ), introduced to these islands through trade in rooted plants from Australasia in the 19th century. It was actually first described from specimens found on the Scilly Isles. It is also found in Devon and Cornwall and other locations, including in Ireland. Pretty benign little creature, feeding on decaying vegetation so nothing to worry about

Thank you very much for your help, Rory. I have searched photos of the creatures you name and I believe you are correct. I have observed them along side plants in the greenhouse and they dont appear interested so I am more than happy to leave them be. They may however be at risk from the resident frogs.